Figure shows blood circulation in humans with labels A

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Figure shows blood circulation in humans with labels A to D. Select the option which gives correct identification of label and functions of the part:

1. A – Artery - thick walled and blood flows evenly
2. B – Capillary - thin without muscle layers and wall two cell thick
3. C – Vein - thin walled and blood flows in jerks/spurts
4. D – Pulmonary vein - takes oxygenated blood to heart PO₂ = 95 mmHg

Correct Option: D

Artery is blood vessel which receives blood from heart, has elastic thick wall showing jerky movements due to pumping activity of heart. Vein is a blood vessel which carries blood towards the heart, has wider lumen with internal valves where blood flows smoothly and slowly. Blood capillary is a very fine blood vessel which has a single layered wall. Pulmonary veins are the only veins which carry oxygenated blood. (PO₂ = 95 mmHg, PCO₂ = 40 mmHg)